(a) Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing the same, and more particularly to a semiconductor device having a highly reliable wiring conductor film and a method for manufacturing the same.
(b) Description of the Prior Art
As conventional wiring conductor film materials used in a semiconductor device, aluminum alloys doped with a small amount of copper, silicon or precious metals have been known.
A copper-doped aluminum conductive stripe is disclosed in U.S. Pat. No. 3,725,309, and is indicated to be advantageous against electromigration, in other words, to be effective in preventing disconnection failures in conductive film interconnections due to electrical drift.
According to the above U.S. Pat., in order to avoid the problems due to electromigration, copper (Cu) in an amount of 0.1 to 54 weight is added to aluminum (Al). Thereby precipitation structure of CuAl.sub.2 grains is formed, the same interposes in grain boundaries and intercrystal triple points of aluminum base, restrains atom movement of aluminum atoms, and prolongs a life span of a semiconductor device while suppressing the electromigration.
However, as CuAl.sub.2 is likely to segregate, so that there is a drawback that a failure due to electromigration occurs at portions where CuAl.sub.2 is not precipitated.
Moreover, it is difficult to process an AlCu alloy into a conductive film pattern by means of dry-etching. As the same is corroded with chlorine (Cl) elements in use and residual Cl ions, the same is attended with a drawback in that it is extremely difficult to process the same with a precision of less than 1.mu.m, in particular less than 0.6 .mu.m.
Besides, a little amount of silicon and moreover a precious metal (Pt, Pd, Rh, In) doped aluminum conductor film material is disclosed in Japanese Patent Application, Laid-Open No. 60-26640 (1986), and Japanese Patent Application Laid-Open No. 61-144817 (1986), however the same is attended with the same drawback as in the above U.S. Pat.
Further, so as to enhance electromigration resistance property, a laminated wiring conductive film which is composed of an aluminum alloy and a high fusing point metal is discussed in IEEE, IRPS (1988) pp. 179-184.
This is because such prevents disconnection of the wiring conductor as a whole, due to the laminated high fusing point metal even when an aluminum alloy be disconnected due to electromigration.
More specifically, as laminated wiring conductor films having an aluminum alloy and a high fusing point metal, there are mentioned AlCu alloy/MoSi.sub.2 and AlSi alloy/TiW. However, the specific resistance of MoSi.sub.2 is about 800 .mu..OMEGA.cm, that of TiW is 60-100 .mu..OMEGA.cm, and these are about 20 to 300 times higher than that of an Al alloy (30 .mu..OMEGA.cm). Therefore, when an Al alloy is disconnected, the temperature of MoSi.sub.2 or TiW increases, causing another disconnection.
Moreover, the above laminated-layer conductor film permits a current density of only 1 to 2.times.10.sup.2 A/cm.sup.2, which is not sufficient for a current density of more than 5.times.10.sup.5 A/cm.sup.2 required for a semiconductor device incorporating a microscopic conductor film (less than 0.6 .mu.m) to meet with ever increasing memory capacity.
In the above-mentioned prior art, measures for improving electromigration resistance in aluminum alloys and lowering electrical resistance in laminated conductor films were not examined sufficiently.
Resistance increase in the laminated conductor film due to electromigration results from disconnection at grain boundaries, which is caused by migration, or mass transport of aluminum over a layer of MoSi.sub.2 or TiW (hereinafter referred to as a barrier layer) during current conduction. When grain boundaries are strong enough, an increase in resistance will not occur.
However, since the specific resistances of MoSi.sub.2 and TiW are approximately 20 to 300 times larger than that of aluminum, when the electromigration resistance of aluminum is insufficient, the resistance of the conductor film will inevitably increase owing to the disconnection of aluminum, thereby leading to a disconnection of the laminated conductor film. Because the electromigration resistance property of an AlCu alloy now in use is not enough, the same has a problem wherein the resistance of the conductor film is increased through a large electric current conduction.
When aluminum alloys doped with several percent of silicon are used for wiring in a semiconductor device, and this device is operated under a large current or at a high temperature, constituent atoms in the aluminum alloy conductor film are migrated, due to a current flowing therein, forming a hillock in one section and a void in another section. When the hillock grows the same causes a short-circuiting, when the voids grows the same causes an electrical resistance increase in the wiring conductor, consequently fusing the same by the heat generated, finally leading to a failure of the semiconductor device.
Prior publications other than above relating to wiring conductor thin films, are Japan Patent Application, Laid-Open No. 55- 56645 (1980), Japan Patent Application, Laid-Open No. 59- 61147 (1984), Japan Patent Application, Laid-Open No. 59- 28360 (1984) Japan Patent Application, Laid-Open No. 63-4649 (1988), and Japan Patent Application, Laid-Open No. 133648 (1988).